The present invention relates to a fixture for enabling the measurement of carbon dioxide (CO.sub.2) or other gases that can flow through or leak from container closures; more particularly, the invention relates to an apparatus for securely holding a container and for sealing about the container neck and closure cap to facilitate the measurement of carbon dioxide or other gases which escape through the closure.
Certain apparatus for measuring vapor flow rates using particular sensor devices are known in the prior art. One type of sensor device typically provides an infrared signal variation if a chamber in response to the presence of carbon dioxide gas in the chamber. One such detector is disclosed in U.S. Pat. No. 3,901,820, Aug. 26, 1975, "Pressure Modulated Gas Measuring Method and Apparatus."
Other types of sensors utilize predetermined wavelengths of radiated energy to detect the presence of certain vapors or gases, as for example, coulimetric detectors for detecting the presence of oxygen.
It is usually desirable to make measurements with these devices under equilibrium conditions, where a vapor or gas is confined within the container, and a vapor or gas detector is connected to a chamber which encloses the container, and an inert carrier gas such as nitrogen is passed through the chamber to convey the leakage vapor or gas to a sensor capable of measuring small quantities of leakage gas. The overall objective of such tests is to obtain a quantitative value which provides a measure of the effectiveness of the container to retain the gases it initially holds. For example, a soft drink container is initially filled with a quantity of liquid and carbon dioxide gas to provide the carbonization associated with a fresh soft drink. The ability of the container to retain the carbon dioxide gas controls the shelf life of the soft drink, for the soft drink tastes flat after a sufficient quantity of the carbon dioxide gas has escaped from inside the container.
It can be appreciated that glass containers which were formerly widely used in the soft drink and related industries provided an exceedingly long shelf life for the products they contained. Leakage of carbon dioxide from these containers is limited to leakage around the closure cap, which typically is very insubstantial. More recently, use of plastic containers for soft drinks has provided a renewed interest in measuring the rate at which carbon dioxide escapes from containers, Further, use of new and different closure caps in combination with plastic containers has also presented new problems in measuring the amount of gas which escapes from the closure cap and the closure cap seal against the plastic container. The newest form of soft drink container frequently has a plastic bottle with a threaded neck, and a threaded closure cap tightened over the threaded neck to seal the bottle. It has become necessary to measure the gas leakage through the body of the plastic container, and also leakage through the closure cap and the region around the closure cap seal against the container.